U.S. patent application number 13/713247 was filed with the patent office on 2013-06-27 for pulley assembly with a decoupling mechanism.
The applicant listed for this patent is Paul T. McCrary. Invention is credited to Paul T. McCrary.
Application Number | 20130161150 13/713247 |
Document ID | / |
Family ID | 48613155 |
Filed Date | 2013-06-27 |
United States Patent
Application |
20130161150 |
Kind Code |
A1 |
McCrary; Paul T. |
June 27, 2013 |
PULLEY ASSEMBLY WITH A DECOUPLING MECHANISM
Abstract
Various pulley assemblies are described that include a pulley
body, a hub defining an axis of rotation disposed within a bore of
the pulley body, and an actuator and a clutch mechanism disposed
about the hub. The actuator axially expands when the pulley body
rotates in a predominant direction, and the clutch mechanism is
activated thereby into an engaged position. In this engaged
position, the clutch mechanism links the pulley body to the hub for
simultaneous rotation in the predominant direction. Then, when the
pulley body rotates in a non-dominant direction or experiences a
deceleration, the pulley assembly enters an overrun position where
the clutch mechanism disengages and allows the hub to rotate at
speeds greater than the pulley body. Additionally, a reverse
configuration is described where the actuator axially expands when
the hub rotates and the clutch mechanism, when engaged, links the
hub to the pulley body.
Inventors: |
McCrary; Paul T.;
(Belleville, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
McCrary; Paul T. |
Belleville |
MI |
US |
|
|
Family ID: |
48613155 |
Appl. No.: |
13/713247 |
Filed: |
December 13, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61576487 |
Dec 16, 2011 |
|
|
|
Current U.S.
Class: |
192/41R ;
192/103R; 192/66.2; 192/70.23; 192/89.2; 192/93R; 192/94 |
Current CPC
Class: |
F16D 2023/123 20130101;
F16D 13/76 20130101; F16D 43/04 20130101; F16D 41/22 20130101; F16D
13/28 20130101; F16D 23/12 20130101; F16H 55/36 20130101; F16D
13/54 20130101 |
Class at
Publication: |
192/41.R ;
192/103.R; 192/93.R; 192/94; 192/89.2; 192/66.2; 192/70.23 |
International
Class: |
F16D 43/04 20060101
F16D043/04 |
Claims
1. A pulley assembly comprising: a pulley body having a bore; a hub
defining an axis of rotation disposed within the bore of the pulley
body; an actuator disposed about the hub, the actuator capable of
axial expansion when the pulley body rotates in a predominant
direction; and a clutch mechanism disposed about the hub, the
clutch mechanism being activatable into an engaged position by the
axial expansion of the actuator; wherein in the engaged position
the axial expansion of the actuator activates the clutch mechanism,
which links the pulley body to the hub for simultaneous rotation in
the predominant direction.
2. The pulley assembly of claim 1 wherein the actuator includes a
ramp-ramp unit, a roller-ramp unit, a cam-follower unit, or a
ball-screw unit that expands axially when the pulley body rotates
in the predominant direction.
3. The pulley assembly of claim 2 wherein the actuator includes the
roller-ramp unit, the roller-ramp unit having one or more roller
elements disposed between an upper ramp component and a lower ramp
component.
4. The pulley assembly of claim 2 wherein the one or more roller
elements are spherical, uniformly cylindrical, or tapered
cylindrical bearings.
5. The pulley assembly of claim 2 further comprising a biasing
member biasing the components of the actuator axially into
maintained contact during operation of the pulley assembly.
6. The pulley assembly of claim 5 wherein the biasing member is
disposed between the actuator and a cap or between the actuator and
the clutch mechanism.
7. The pulley assembly of claim 5 wherein the biasing member
includes one or more Belleville washers.
8. The pulley assembly of claim 5 wherein the biasing member is a
coil spring disposed between an upper ramp component and a lower
ramp component.
9. The pulley assembly of claim 1 wherein the clutch mechanism
includes a clutch pack or a cone clutch.
10. The pulley assembly of claim 9 wherein the clutch mechanism is
the clutch pack and the clutch pack includes at least one clutch
plate and at least one friction disc.
11. The pulley assembly of claim 10 wherein either the clutch plate
or the friction discs are coupled to the hub for rotation therewith
while being translatable therealong and the other is coupled to the
actuator for rotation therewith while being translatable along the
hub.
12. The pulley assembly of claim 1 wherein when the pulley body
rotates in a direction opposite the predominant direction or
experiences a deceleration, the clutch mechanism disengages from
the actuator and allows the hub to rotate independently of the
pulley body in the predominant direction under its own
momentum.
13. The pulley assembly of claim 2 wherein the clutch mechanism
includes a clutch pack or a cone clutch.
14. The pulley assembly of claim 1 wherein when the pulley body
rotates in a direction opposite the predominant direction or
experiences a deceleration, the pulley assembly enters an overrun
position where the clutch mechanism disengages from the actuator
and allows the hub to rotate at speeds greater than the pulley
body.
15. The pulley assembly of claim 2 wherein the actuator is a ball
screw comprising a nut coupled to the pulley body for rotation
therewith and being translatable relative thereto, a threaded shaft
about which the nut is disposed, and a plurality of rolling
elements recirculating within a raceway defined between the nut and
the threaded shaft.
16. The pulley assembly of claim 1 wherein the actuator provides
isolation from and damping of torsional excitations.
17. A pulley assembly comprising: a pulley body having a bore; a
hub defining an axis of rotation disposed within the bore of the
pulley body; an actuator disposed about the hub, the actuator
capable of axial expansion when the hub rotates in a predominant
direction; and a clutch mechanism disposed about the hub, the
clutch mechanism being activatable into an engaged position by the
axial expansion of the actuator; wherein in the engaged position
the axial expansion of the actuator activates the clutch mechanism,
which links the hub to the pulley body for simultaneous rotation in
the predominant direction.
18. The pulley assembly of claim 17 wherein when the hub
experiences a deceleration, the pulley assembly enters an overrun
position where the clutch mechanism disengages from the actuator
and allows the pulley body to rotate at speeds greater than the
hub.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. provisional
Application No. 61/576,487 filed Dec. 16, 2011.
TECHNICAL FIELD
[0002] The present application relates generally to pulleys and
more particularly to a pulley assembly that includes a decoupling
mechanism.
BACKGROUND
[0003] It is known to drive various automobile accessory
assemblies, including for example a water pump, an
alternator/generator, a fan for cooling coolant, a power steering
pump, and a compressor, using the vehicle engine. In particular, a
driving pulley actuated by an engine shaft of the motor vehicle
drives an endless drive belt that in turn drives the accessory
assemblies through driven pulleys.
[0004] Periodic torque pulses initiated by, for example, combustion
engine firing can create significant speed transitions which can
interrupt smooth operation of the driven components. In addition,
inertial and driven speed transitions associated with startup,
shutdown, jake braking, gear shifting, etc. can also interrupt
operation of the driven components. These transitions can result in
undesirable effects such as belt jump, belt wear, bearing wear,
noise, etc.
[0005] The engine, driving belt system, and driven accessory are
comprised of primary and additional driving/driven speeds and
frequencies. These are characteristic of the system and usually
will meet desired operating targets while being relatively stiffly
connected by the belt drive system. However at some operating
points and/or conditions these speeds and frequencies contribute to
unwanted noise, compromise system or component integrity, or
contribute to reduced service life of the belt system or individual
component. Current solutions provide for overrunning of an
accessory exist and others provide for torsional isolation, but
improvements are needed that outperform, last longer, and are more
cost effective to manufacture.
SUMMARY
[0006] Improved driven or driver pulley assemblies are disclosed
that utilize torque-sensitive coupling and de-coupling to permit
one-way relative motion between an input shaft of a driven
accessory and an outer driven sheave of the pulley assembly or
between a crank shaft and an outer drive sheave of the pulley
assembly.
[0007] For a driven pulley assembly, when the sheave of the pulley
assembly is being driven in the predominant direction of rotation,
the clutching mechanism of the pulley assembly engages and drives
the accessory input shaft for the desired smooth rotation. When
relative torque reversals occur as a result of, for example, driven
speed transitions, the internal clutching mechanism of the proposed
pulley assembly disengages the driven accessory shaft from the
outer driven sheave, thereby permitting the driven shaft to
continue to rotate with momentum in the predominant direction of
rotation even at speeds greater than the driven sheave of the
pulley.
[0008] For a driver pulley assembly, when the hub of the pulley,
which is coupled to a crank shaft, is rotated in the predominant
direction of rotation, the clutching mechanism of the pulley
assembly engages and drives the sheave of the pulley assembly for
the desired smooth rotation. When relative torque reversals occur
as a result of, for example, crank shaft speed transitions, the
internal clutching mechanism of the proposed pulley assembly
disengages the sheave of the pulley assembly from the hub (crank
shaft), thereby permitting the sheave of the pulley to continue to
rotate with momentum in the predominant direction of rotation even
at speeds greater than the hub or crank shaft.
[0009] In one aspect, belt drive assemblies for driving belt driven
accessories in an engine of an automotive vehicle, and more
particularly, to a decoupling mechanism for allowing the belt
driven accessories to operate temporarily at a speed other than the
belt drive assembly are also provided. Here the belt drive assembly
includes the improved driven pulley described above, at least one
driver pulley, and an endless belt entrained about both pulleys. In
another embodiment, the belt drive assembly may include the
improved driver pulley at the crank shaft, at least one driven
pulley and an endless belt entrained about both pulleys. In yet
another embodiment, the belt drive assembly may include the
improved driver pulley at the crank shaft, the improved driven
pulley, and an endless belt entrained about both pulleys.
[0010] The pulley assemblies disclosed herein provide both
overrunning and decoupling capability that exceeds current
performance and maintains the level of practicality demanded by the
automotive industry. In one embodiment, the pulley assembly
includes a pulley body having a bore, a hub defining an axis of
rotation disposed within the bore of the pulley body, and an
actuator and a clutch mechanism disposed about the hub. The
actuator is capable of axial expansion when the pulley body rotates
in a predominant direction and the clutch mechanism is activated,
moved into an engaged position, by the axial expansion of the
actuator. This engaged position links the hub to the pulley body
for simultaneous rotation in the predominant direction. Then, when
the pulley body rotates in a direction opposite the predominant
direction or experiences a deceleration, the clutch mechanism
disengages from the actuator and allows the hub to rotate
independently of the pulley body, still, in the predominant
direction under its own momentum. In other words, the pulley
assembly enters an overrun position where the clutch mechanism
disengages from the actuator and allows the hub to rotate at speeds
greater than the pulley body.
[0011] The actuator within the pulley assembly may be a ramp-ramp,
roller-ramp, ball-ramp, cam follower, or ball screw unit that
expands axially when the pulley body rotates in the predominant
direction. If the actuator is the roller-ramp unit, the roller-ramp
unit includes one or more roller elements disposed between an upper
ramp component and a lower ramp component. If the actuator is a
ball screw unit, the ball screw unit includes a nut coupled to the
pulley body for rotation therewith and being translatable relative
thereto, a threaded shaft about which the nut is disposed, and a
plurality of rolling elements recirculating within a raceway
defined between the nut and the threaded shaft.
[0012] The clutch mechanism within the pulley assembly may be a
clutch pack or a cone clutch. If it is the clutch pack, it includes
at least one clutch plate and at least one friction disc and either
the clutch plate or the friction disc are coupled to the hub for
rotation therewith while being translatable therealong and the
other is coupled to the actuator for rotation therewith while being
translatable along the hub.
[0013] The pulley assembly may also include a biasing member that
biases the components of the actuator axially into maintained
contact during operation of the pulley assembly. The biasing member
may be disposed between the actuator and a cap or between the
actuator and the clutch mechanism. In one embodiment, the biasing
member includes one or more Belleville washers. In another
embodiment, the biasing member is a coil spring.
[0014] In an embodiment where the pulley assembly is a driver
pulley mounted to a crank shaft, the actuator is coupled to the hub
for axial expansion in response to the rotation of the hub and the
clutch mechanism is activated by the axially-expanding actuator
into an engaged position that couples the hub to the pulley body
for simultaneous rotation together. Then, when the clutch mechanism
is decoupled in response to the contraction of the actuator, the
pulley assembly "overruns" and allows the pulley body to continue
to rotate under its own momentum at speeds greater than those of
the hub (and crank shaft).
[0015] Advantages and features of the invention will be apparent
from the following description of particular embodiments and from
the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a diagrammatic view of an embodiment of an
accessory drive system.
[0017] FIG. 2 is an exploded, perspective view of one embodiment of
a pulley assembly for use in an accessory drive system such as that
illustrated in FIG. 1.
[0018] FIG. 3 is a side, section view of the pulley assembly of
FIG. 2.
[0019] FIG. 4 is an exploded, perspective view of a second
embodiment of a pulley assembly for use in an accessory drive
system such as that illustrated in FIG. 1.
[0020] FIG. 5 is a side, section view of the pulley assembly of
FIG. 4.
[0021] FIG. 6 is an exploded, perspective view of a third
embodiment of a pulley assembly for use in an accessory drive
system such as that illustrated in FIG. 1.
[0022] FIG. 7 is a side, section view of the pulley assembly of
FIG. 6.
[0023] FIG. 8 is a perspective view of a portion of the actuator
included in the pulley assembly of FIG. 6.
[0024] FIG. 9 is an exploded, perspective view of one embodiment of
a pulley assembly for use in an accessory drive system such as that
illustrated in FIG. 1.
[0025] FIG. 10 is a side, section view of the pulley assembly of
FIG. 9.
[0026] FIG. 11 is a sectional view of one embodiment of a ramp
plate as illustrated in FIG. 9.
[0027] FIG. 12 is an exploded, perspective view of an alternate
embodiment of the pulley assembly of FIG. 2 for use in an accessory
drive system such as that illustrated in FIG. 1.
[0028] FIGS. 13A and 13B are side, perspective views of the clutch
actuator of the pulley assembly in FIG. 12 illustrating an
assembled position (FIG. 13A) and a maximum travel position (FIG.
13B).
[0029] FIG. 14 is a graph of a damper curve for the pulley assembly
of FIG. 12.
[0030] FIG. 15 is an exploded, perspective view of an alternate
embodiment of the pulley assembly of FIG. 2 for use in an accessory
drive system such as that illustrated in FIG. 1.
[0031] FIG. 16 is an assembled, cross-sectional view of the pulley
assembly of FIG. 15.
[0032] FIG. 17A is a sub-assembly of the actuator and drive plate
within the pulley assembly of FIG. 15.
[0033] FIG. 17B is an exploded perspective view of the sub-assembly
of FIG. 17A.
DETAILED DESCRIPTION
[0034] The following detailed description will illustrate the
general principles of the invention, examples of which are
additionally illustrated in the accompanying drawings. In the
drawings, like reference numbers indicate identical or functionally
similar elements.
[0035] Referring to FIG. 1, an accessory drive system 10 of, for
example, an internal combustion engine of an automobile includes an
endless belt 30 that is used to drive a number of accessories. The
various accessories are represented in FIG. 1 diagrammatically by
their pulley assemblies. The belt 30 is entrained around a crank
pulley assembly 12, a fan/water pump pulley assembly 14, a power
steering pulley assembly 18, an idler pulley assembly 20 and a
tensioner pulley assembly 22. In some embodiments, the tensioner
pulley assembly 22 includes damping, such as asymmetric damping
with a frictional damper to resist lifting of the tensioner arm
away from the belt 30.
[0036] The various accessories are driven through use of pulley
assemblies 14, 16, 18, 20 and 22 that are themselves rotated by the
belt 30. For purposes of description, pulley assembly 16 of an
alternator will be focused on below. It should be noted, however,
that the other pulley assemblies of one or more of the other
accessories may also operate in a fashion similar to that of pulley
assembly 16.
[0037] Referring now to FIGS. 2 and 3, pulley assembly 16 transfers
input torque from the belt 30 to the input shaft 78 of an
accessory, for example an alternator or fan, when rotated in a
predominant rotational direction and also isolates the input shaft
78 from relative torque reversals between the pulley assembly 16
and the input shaft 78. When such relative torque reversals between
the pulley assembly 16 and the input shaft 78 occur, an internal
decoupler system of the pulley assembly 16 acts to disengage the
input shaft 78 from the torque reversal, also referred to as an
overrunning condition, thereby permitting the accessory input shaft
78 to continue rotating with momentum in the predominate
operational direction.
[0038] The pulley assembly 16 includes a hub 40 that is engageable
with the input shaft 78 of the accessory, a roller bearing 42, a
one-way clutch mechanism 44, a friction ring 46, a clutch actuator
48, a biasing member 50, and a closure member 52 (or cap) that are
all housed within the bore 54 of a pulley body 56. The hub 40 may
be mated to the input shaft 78 by a Woodruff key, as is well known,
to prevent the hub 40 from freely rotating about the input shaft.
Of course other connections between the hub 40 and the input shaft
78 are also possible including, for example, a spline. The roller
bearing 42 may be located between the hub 40 and the pulley body 56
to permit stable rotation of the pulley body 56 relative to the hub
40 when disengaged. The inner race 64 of the roller bearing 42 may
be adjacent and coupled to the hub 40. The outer race 66 of the
roller bearing 42 may be adjacent and coupled to the pulley body
56. The use of a roller bearing may improve the overall structural
rigidity of the assembly and extend the life of the assembly by
reducing wear as elements of the clutching mechanism rotate
relative to one another.
[0039] As illustrated in FIGS. 2 and 3, the pulley body 56 is
located about the hub 40 and includes a central bore or opening 54
that is sized such that the pulley body can rotate about the hub.
The pulley body 56 also includes an outer, peripheral belt-engaging
surface 58 that engages belt 30 (FIG. 1), and a coupling feature 59
within the inner surface 62 that defines the bore 54. In the
illustrated embodiment, the belt engaging surface 58 is profiled
including V-shaped ribs and grooves to mate with corresponding ribs
and grooves on the belt 30. Other configurations are possible, such
as cogs, flat or rounded ribs and grooves. The coupling feature 59
on the inner surface 62 (most easily seen in FIG. 2) may be
grooves, pathways, slots, keyways, or the like recessed into the
inner surface 62. Alternately, the coupling feature 59 may be a
protrusion, tab, key, splines, or the like on the inner surface 62
that protrude or extend inward (toward the axis of rotation). The
coupling feature 59 is configured to engage a mating coupling
feature 102 on a member of the clutch actuator 48. The engagement
of the mating coupling feature 102 with the coupling feature 59
provides for rotation of the pulley body 56 with a member of the
clutch actuator (i.e., transfer torque from the pulley body 56 to
other components).
[0040] The clutch actuator 48 includes a ramp construction or a
roller-ramp construction that expands axially (i.e., has at least
one component that is translatable along the axis of rotation 49 to
a location that is further from another component thereof) as a
result of rotational movement of at least a portion of the clutch
actuator. The axial expansion typically is a result of one
component moving up or along an inclined feature or moving in
response to the movement of a rolling element up or along an
inclined feature. The use of the clutch actuator 48 to actuate the
one-way clutch mechanism 44 provides the pulley assembly 16 with
isolation or damping capability. The clutch actuator in the
embodiment of FIGS. 2 and 3 includes an upper ramp component 80 and
a lower ramp component 82 with a roller element 84 enclosed
therebetween. Upper and lower are used herein as relative to
positions of the components of the pulley assembly 16 as
illustrated in FIG. 3 with respect to the orientation of the page.
The terms upper and lower are likewise applicable to the other
drawings herein. The upper ramp component 80 is generally located
adjacent to the spring 50, which is illustrated as a Belleville
washer, and the lower ramp component 82 is generally located
adjacent to the other components of the one-way clutch mechanism
44.
[0041] The upper ramp component 80 has a generally smooth upper
surface 90, a lower surface 92 comprising one or more first
inclined features 94 recessed into the body 96 of the upper ramp
component 80, an inner surface 98 defining a bore for receiving the
hub 40, and an outer surface 100 having one or more mating coupling
features 102. In the assembled state (FIG. 3), the upper ramp
component 80 is coupled to the pulley body 56 by engaging the
mating coupling features 102 with the coupling features 59 in the
pulley body 56. Accordingly, the upper ramp component 80 is fixed
to the pulley body 56 for rotation therewith, but is free to
translation relative thereto while maintaining engagement of the
coupling features 59, 102. The pulley assembly 16 is constructed
such that when the upper ramp component 80 translates relative to
the pulley body 56, the coupling features 59, 102 provide
frictional contact therebetween, which provides beneficial coulomb
damping.
[0042] The first inclined features 94, best seen in FIG. 2, define
a channel within which a roller element 84 is seated. The channel
has a first end 103 that is shallow relative to a second end 104
(i.e., the second end is recessed more deeply into the body 96 of
the upper ramp component 80). For smooth angular displacement of
the upper ramp component 80 (and rotation of the roller element 84)
the channel is preferably smoothly, gradually tapering from the
first end 103 to the second end 104.
[0043] The lower ramp component 82 has an upper surface 110
comprising one or more second inclined features 112 recessed into
the body 114 of the lower ramp component 82, a generally smooth
lower surface 116, an inner surface 118 defining a bore for
receiving a friction ring 46, which together receive the hub 40,
and a generally smooth outer surface 120. The lower surface 116
includes one or more tabs 122 extending axially downward away from
the lower surface. The tabs 122 are positioned generally proximate
to the outer surface 120 of the lower ramp component 82 and create
a corral to contain one or more components of the one-way clutch
mechanism 44, in particular a clutch pack 130 (FIG. 3). The second
inclined features 112 are similarly constructed to those in the
upper ramp component 82, except that the orientation of the first
end and second end of the second inclined features 112 is reversed
relative to the orientation of the first and second ends 103, 104
of the first inclined features 94.
[0044] The roller elements 84 received in opposing first and second
inclined features 94, 112 may be cylinders, balls, generally
conical cylinders, or the like.
[0045] The friction ring 46 is fixed to the lower ramp component 82
such that they rotate together. As assembled in FIG. 3, the
friction ring 46 rubs against the shaft portion 41 of the hub 40
during rotation. This frictional contact retards the motion of the
lower ramp component relative to the pulley body 56 thereby
allowing the upper ramp component 80 and the lower ramp component
82 to not rotate together. This creates circumferential divergence
where both can still rotate, but in opposite directions and not
necessarily at the same speed. This relative rotation will move the
roller elements 84 within, up, or along the first and second
inclined features 94, 112 to axially translate the first and second
ramp components relative to one another.
[0046] The axial expansion of the actuator 48 during rotation of
the pulley body 56 in the predominate rotational direction actuates
the one-way clutch mechanism 44 which couples the pulley body 56 to
the hub 40 to transmit power from the belt 30 (FIG. 1) to the input
shaft 78 (FIG. 2) of an accessory. The one-way clutch mechanism 44
includes a plurality of alternating friction discs 130 and friction
core plates 132. Each friction disc 130 and friction core plate 132
has a bore therethrough to receive the shaft 41 of the hub 40.
[0047] The pulley assembly 16 also includes a biasing element 50
(FIGS. 2 and 3) that becomes compressed as the ramp-ramp,
roller-ramp, cam follower, or ball screw components expand, in
particular, as the upper and lower ramp components 80, 82 axially
expand apart. The compression of the biasing element 50 translates
to a torsion rate across the device. Coulomb damping, described
above, is created by the friction between the upper ramp component
80 sliding against the pulley body 56 during stroke of the spring
and as the friction ring 46 slides against the hub 41. Thus, the
input and output are decoupled, or isolated, from torsional
excitations, generally of the input, by this roller-ramp/spring
damper configuration. Spring rate can be varied, through selection
of spring, to match system requirements. The ramp or include angle
or profile can be modified to enhance and/or tailor isolation
characteristics.
[0048] Interposed between the actuator 48 and the roller bearing 42
is a clutch 44 that includes a clutch pack 130. As shown in FIG. 2,
the clutch pack includes alternating friction discs 131 and
friction core plates 132. The friction discs 131 have an inner
diameter that defines a surface that includes a key or keyway for
mating engagement with the hub 40 for rotation therewith. In one
embodiment the friction discs 131 and the hub 40 have a splined
connection. The friction core plates 132 include a key, keyway,
tabs, splines, cogs, or the like 134 in the surface defining its
outer diameter. The cogs 134 are received between tabs 122 on the
lower ramp component 82 and similarly configured second tabs 136 on
holder 140 to form a cage or corral around the clutch pack 130.
[0049] The pulley assembly 16, in particular the hub 40 thereof,
defines an axis of rotation 49 as labeled in FIG. 3. When the
one-way clutch mechanism 44 is engaged, the pulley body 56 rotates
the input shaft 78 of the accessory. The engaged position is
achieved by angular displacement provided through the relative
rotation of the pulley body 56 and the component(s) of the actuator
48 that are rotationally fixed to the pulley body. In FIGS. 2 and
3, the upper ramp component 80 is fixed to rotate with the pulley
body. Rotation of the upper ramp component 80 via rotation of the
pulley body 56 moves the roller element 84 within the inclined
features 94, 112, which expands the actuator by translating the
upper and lower ramp components axially. This axial translation
compresses biasing member 50, which in turn urges all the
components of the actuator 48 to translate axially toward the
clutch 44 to compress the clutch pack 130 for increased frictional
engagement between the friction disc 130 and the friction core
plate 132. Once the clutch pack 130 is compressed into a frictional
engagement that allows all the components of the clutch pack to
rotate together as a unit, the hub 40, which is coupled to the
friction discs 130 for rotation therewith, will rotate with the
pulley body 56. This is the engaged position of the clutch.
[0050] During an overrunning condition, the input shaft 78
disengages from the pulley assembly, in particular from the pulley
body 56, and continues to rotate with momentum in the first
rotational direction (the predominant direction) when the pulley
body 56 experiences a relative torque reversal or sudden slowdown.
In this condition, the pulley body 56 may continue to rotate in the
first rotational direction but with less angular velocity than the
velocity at which it had been driving the input shaft 78. The
sudden decrease of angular velocity at the pulley body 56 has the
effect of a relative reversal of torque, which rotates at least one
component of the actuator 48 through rotation of the pulley body 56
to compress the actuator (i.e., reduce the axially expansion of the
actuator), which relieves the clutch 44 of the compressive forces
that moved it into an engaged position. As the contact pressure and
friction force between the actuator 48 and the clutch 44 decrease,
they will eventually disengage the clutch 44, which uncouples the
pulley body 55 from the hub 40 so that they can rotate relative to
one another with minimal friction such that the input shaft 78
rotates independently of the pulley body 56.
[0051] FIG. 12 is an alternate embodiment of the pulley assembly
16. Here, like components have the same reference numbers as those
used in FIG. 2. One addition to the embodiment in FIG. 12 is the
inclusion of stops on the lower and upper ramp components 80, 82.
As seen in FIGS. 12-13B, bottom stops 160 and top stops 162, which
limit the travel of the rolling elements 84 and hence the axial
displacement of the lower ramp component 82 relative to the upper
ramp component 80, are present. The bottom stops 160 and top stops
162 are, as their names suggest, positioned at either the bottom of
the inclined features 94 or 112 of the upper ramp component 80 and
lower ramp component 82, respectively. The stops 160, 162 provide a
torque limiter function to the pulley assembly 16, which is
beneficial because it limits the torque applied to the input shaft
78 (shown in FIG. 2) should a high torque transient occur elsewhere
in the system 10 (FIG. 1); thus, protecting an accessory connected
to the shaft 78 from possible damage. Should the accessory be the
source of this high torque transient, the system 10 and belt 30 are
protected. For example, damage to bearings, etc. elsewhere in the
drive system 10 is minimized or avoided. Torque limiting may also
reduce incidence of belt jump. The maximum expansion of the
actuator 48, referring back to FIGS. 12-13B, afforded by the stops
160, 162, limits the forces within the pulley assembly 16 to a
level determined by the compression of the spring(s) 50. This
limited internal force thereby limits the torque capacity of the
clutch, beyond which slippage will occur and system protection is
provided. Whether the high torque transient originates in the
system or accessory, internal damage to the drive pulley 16 is
precluded.
[0052] Another difference within the embodiment shown in FIG. 12 is
that the lower ramp component 82 has cogs 123 as part of the outer
surface thereof rather than tabs 122 as seen in FIG. 2. The cogs
123 connect the lower ramp component 82 to the holder 140 when the
pulley is assembled by fitting between the tabs 136 of the holder
140. Adjacent cogs 123 are separated from one another by a gap 125
(see FIGS. 13A and 13B) dimensioned to receive the tabs 36 of the
holder 140.
[0053] Another difference in the embodiment in FIG. 12, is that a
plurality of biasing members 50 (for example a Belleville washer)
are present. As illustrated, six biasing members are present, but
any number of biasing members can be present such as one, two,
three, four, five, six, seven, eight, etc. A plurality of biasing
members is also shown in FIGS. 7 and 15. The number of biasing
members 50 affects the damping characteristics and spring rate of
the pulley assembly 16. As seen in the graph in FIG. 14, a change
in the number of springs or a change in the overall assembly
stiffness, as a result of altering the spring rate of the springs
(use stiffer springs), changes the damper curve (isolation curve).
The ascending lines illustrate, during rotation in the predominant
direction, that friction is resisting the rotation and that the
torque required to rotate the pulley assembly in the predominant
direction is increased by the friction amount present during
rotation. The change in the slope of each line in FIG. 14 is
achieved because there is more than one spring present, in series,
within the pulley assembly. Initially all springs of the assembly
compress (amount determined by individual stiffness). Assembly
stiffness, or spring rate, is less than any individual spring
(since they are in series). As load increases on the pulley
assembly, an individual spring may lose ability to compress further
(in this case a Belleville spring goes `flat`--against the end cap
52 (FIG. 12) or drive plate 80. Once a spring goes `flat` it no
longer contributes to load change. The remaining spring(s) then
determine load change but at a higher rate, hence the steeper
slope.
[0054] The pulley assembly 16 of FIG. 12 also includes a bearing
assembly 324 between the bearing 42 and the holder 140, similar to
the bearing assembly seen in FIG. 4, explained in more detail
below.
[0055] Referring to FIGS. 4 and 5, power input into the pulley
assembly is through the pulley body 314 as it is rotated by its
contact with a belt. Power output is through the hub 301 (that in
use may be affixed to alternator shaft or other accessory shaft).
Support between the pulley body 314 and the hub 301 includes
bearing 302 and cap 313. Cap 313 is fixed to the pulley body 314
and includes a load support bushing at its inner diameter, to allow
relative rotation between the hub 301 and the cap 313 and, by
material selection, a controllable portion of Coulomb damping. The
lower ramp plate 311, the roller elements 312, and the upper ramp
surface 315 (shown in FIG. 5) included in the cap 313 comprise a
ball-ramp actuator 320. Relative rotation of the lower ramp plate
311 relative to the cap 313 produces axial displacement, as a
result of the contour of the ramps, between lower ramp plate 311
and the cap 313.
[0056] The lower ramp plate 311, biasing member 310, and top
retainer 309 travel axially to effect clutch actuation. The clutch
in this embodiment is shown as a clutch pack 322 comprising a
plurality of plates 308, but can also be a cone clutch similar to
the cone clutch illustrated in FIGS. 6 and 7. Lower ramp plate 311
is rotatably fixed to the biasing member 310 but is free to
translate axially relative to the biasing member 310. The biasing
member 310 may be any of the biasing members discussed above, but
is not limited thereto. Here, the biasing member 310 is also
rotatably fixed to top retainer 309 but is free to translate
axially relative thereto. This embodiment has a serial connection
that differs from the ramp-ramp embodiment in FIGS. 2 and 3 in that
FIGS. 2 and 3 have a sandwich connection where the outer two items
(the biasing element 50 and cap 52) are rotatably fixed and other
components are free to rotate (sandwich connection). Either
embodiment may be used. Axial displacement of the lower ramp plate
311 contacts and moves the biasing member 310 into contact with top
retainer 309, which in turn axially contacts the clutch pack 22
comprising friction discs 307, friction core plates 308 and bottom
retainer 306. A bearing assembly 324 that includes upper plate 303,
roller element plate 304 and lower plate 305 reacts clutch pack
load to the pulley, through bearing 302. This embodiment, in
addition to having a ball-ramp actuator 320, provides an embodiment
that advantageously has minimal damping characteristic. Minimal
damping is provided through: (1) use of bearing assembly 324; (2)
serial connection of the biasing member 310 to other components;
and (3) having the biasing member and the clutch mechanism on the
same side of the actuator.
[0057] In the embodiment of FIG. 4, the lower ramp plate 311 has an
upper surface 344 that faces a lower surface 346 of the cap 313.
Both the upper surface 344 and the lower surface 346 have ramp
divots 342 that are aligned with each other to allow the rolling
elements 312 to reside in the pockets formed by the ramp divots 342
when the lower ramp plate 311 and the cap 313 are assembled. The
ramp divots 342 have a socket 352 for receiving the rolling element
312 and a divot tail 354 as shown in FIG. 4. The socket 352 has a
depth of at least equal to the dimensions of the rolling elements
312. The divot tail 354 has a first end that starts at a depth
equal to the socket 352 and gradually becomes shallower until a
second end of the divot tail 354 is flush with the upper surface
344 of the lower ramp plate 312, or the lower surface 346 of the
cap 313 depending on the location of the ramp divot 342.
[0058] The ramp construction or roller-ramp construction
illustrated in FIG. 4 may also be described as inclined features as
set forth above for FIGS. 2 and 3.
[0059] Referring to FIGS. 6-8, power input into the pulley assembly
is through the pulley body 201 as it is rotated by its contact with
a belt. Power output is through hub 205 (that in use may be affixed
to alternator shaft or other accessory shaft). Support between the
pulley body 201 and the hub 205 consists of bearing 202 and cap
210. Cap 210 includes a load support bushing at its inner diameter,
to allow relative rotation between the pulley body 201 and the hub
205 and, by material selection, a controllable portion of Coulomb
damping. Cap 210 and cam 208 comprise a ramp-ramp or cam-follower
actuator. As seen in FIG. 8, cap 210 includes, in its inner surface
212, a track or groove 214 that includes hurdles 216 spaced apart
within the track 214. The hurdles 216 may have arcuate ends or ends
having sloped or inclined surfaces facing the cam 208 such that
relative rotation between the cam 208 and the cap 210 produces
axial displacement of the cam 208, as a result of the contour of
the ramp surfaces of the cam moving rotationally along the hurdles
216. Cam 208 includes an upper surface 220 that is contoured to
provide a camming action that results in the axial displacement of
the cam 208 during rotation thereof. The contour may include
alternating, or even undulating, valleys 222 and peaks 224. The
valleys 222 of the contour are located opposite the hurdles 216
when the pulley assembly is in a rest position. Positive input from
the pulley body 201 results in relative rotation in a positive
sense, negative input results in relative rotation in the negative
sense from the rest position. Positive and negative ramp slopes, or
profiles, are shown as identical in FIGS. 6-8, but the assembly is
not limited thereto. In practice these ramp slopes, or profiles on
the hurdles 216 and the contour of the upper surface 220 of the cam
208 may be different slopes or profiles.
[0060] Inner cone ring 207, cam 208 and biasing elements 209
provide axial travel and force to apply a clutch 230 having
cone-shaped members. Cam 208 is rotatably fixed to inner cone ring
207 but is free to translate axially relative thereto. Axial
displacement of cam 208 contacts and moves the biasing elements 209
into contact with the inner cone ring 207, which in turn translates
the inner cone ring 207 axially into contact with intermediate cone
ring 206. Intermediate cone ring 206 translates axially, as a
result, into contact with outer cone ring 203. Outer cone ring 203
is axially and rotatably fixed to the pulley body 201. Additional
displacement of cam 208 will compress biasing members 209. This
compressive force is transmitted to inner cone ring 207 and
intermediate cone ring 206, and then intermediate cone ring 206
frictionally engages the outer cone ring 203. The inner,
intermediate, and outer cone rings 207, 206, 203 and hub connector
204 comprise the clutch 230. The inner cone ring 207 and the outer
cone ring 203 are connected to the input (i.e., the pulley body
201), and the intermediate cone ring 207 and the hub connector 204
are connected to the output (i.e., the hub 205). Intermediate cone
ring 206 is rotatably fixed to the hub connector 204, but is free
to translate axially relative thereto through drive lugs. Hub
connector 204 is rotatably fixed to the output, hub 205.
[0061] The cone clutch in FIGS. 6-8 is illustrated and described as
a two-element clutch, two components are movable. In practice, by
application requirements, this clutch may also be a single-element
or multiple-element clutch. Also the cone element angle is
illustrated as identical on the outer, intermediate, and inner cone
rings 203, 206, 207, but is not limited thereto. In practice, again
by application requirements, the cone angles may be significantly
non equal.
[0062] Referring now to FIGS. 9-11, in one embodiment the pulley
assembly 16 may include a hub 500 that is engageable with the input
shaft of the accessory (not shown, but see FIG. 2 shaft 78), a
roller bearing 502, a one-way clutch mechanism 504, a bushing 506,
a clutch actuator 508, and sealing O-rings 534 that are all housed
within the bore 512 of a pulley body 514. The one-way clutch
mechanism 504 includes friction discs 524, a clutch plate 526, and
a holder 528 for the friction discs 524 and clutch plate 526 (so
that they all rotate as a unit when the one-way clutch is engaged).
The clutch actuator 508 includes a drive plate 510, a ramp plate
522, rolling elements 532, and a preload spring 530. The hub 500
may be mated to the input shaft (not shown) by a Woodruff key, as
is well known, to prevent the hub 500 from freely rotating about
the input shaft. Of course other connections between the hub 500
and the input shaft are also possible including, for example, a
spline.
[0063] The roller bearing 502 may be located between the hub 500
and the pulley body 514 to permit stable rotation of the pulley
body 514 relative to the hub 500 when disengaged. The inner race
516 of the roller bearing 502 may be adjacent and coupled to the
hub 500. The outer race 518 of the roller bearing 502 may be
adjacent and coupled to the pulley body 514. The use of a roller
bearing may improve the overall structural rigidity of the assembly
and extend the life of the assembly by reducing wear as elements of
the clutching mechanism rotate relative to one another.
[0064] As illustrated in FIGS. 9 and 10, the pulley body 514 is
located about the hub 500 and includes a central bore or opening
512 that is sized such that the pulley body can rotate about the
hub. The pulley body 514 also includes an outer, peripheral
belt-engaging surface 520 that can engage a belt such as belt 30 in
FIG. 1. In the illustrated embodiment, the belt-engaging surface
520 is profiled with V-shaped ribs and grooves to mate with
corresponding ribs and grooves of a belt. Other configurations are
possible, such as cogs, flat or rounded ribs and grooves.
[0065] Turning now to the components of the actuator 508, FIG. 9,
the ramp plate 522 has an upper surface 544 that faces a lower
surface 546 of the drive plate 510. Both the upper surface 544 and
the lower surface 546 have ramp divots 542 that are aligned with
each other to allow the rolling elements 532 to reside in the
pockets formed by the ramp divots 542 when ramp plate 522 and drive
plate 510 are assembled. The ramp divots 542 have a socket 560 for
receiving the rolling element 532 and a divot tail 562 as shown in
FIG. 11. The socket 560 has a depth of at least equal to the
dimensions of the rolling elements 532. The divot tail 562 has a
first end 564 that starts at a depth equal to the socket 560 and
gradually becomes shallower until a second end 566 of the divot
tail 562 is flush with the upper surface 544 of the ramp plate 522,
or the lower surface 546 of the drive plate 510 depending on the
location of the ramp divot 542 and thereby defines an inclined
plane along which the rolling elements 352 can roll.
[0066] The ramp construction or roller-ramp construction
illustrated in FIG. 9 may also be described as inclined features as
set forth above for FIGS. 2 and 3 or FIGS. 12-13B.
[0067] As seen in FIG. 9, the upper surface 544 of the lower ramp
plate 522 includes a first recess 548 defining a seat for a first
end 562 of the preload spring 530. Similarly, the lower surface 546
of the drive plate (or cap) 510 includes a second recess (not
shown) defining a seat for a second end 564 of the preload spring
530. When assembled, the first end 562 of the preload spring 530 is
inserted into the first recess 548 in lower ramp plate 522 and the
second end 564 of the preload spring 530 is inserted into the
second recess in the drive plate 510. The rolling elements 532 are
placed within the aligned ramp divots 542 and held between the
drive plate 510 and the lower ramp plate 522. The bias of the
preload spring 530 rotates the lower ramp plate 522 slightly in the
predominate rotational direction relative to the drive plate 510.
As a result, the rolling elements 532 travel slightly up the divot
tail 562. As the rolling elements 532 travel up the divot tail 562,
they push against the drive plate 510 and the lower ramp plate 522,
which results in an axial separation of drive plate 510 and lower
ramp plate 522. Lower ramp plate 522 moves axially towards holder
528. This axial translation moves ramp plate 522 to the right in
FIG. 9 and toward the bottom of the page in FIG. 10, which in turn
urges the friction discs 524 and clutch plate 526 of the one-way
clutch mechanism 504 to translate axially toward the holder 528
resulting in increased frictional engagement between the friction
discs 524 and the clutch plate 526. Once the friction discs 524 are
moved into frictional engagement, all the components of the one-way
clutch mechanism 504 rotate together as a unit so that the hub 500,
which is coupled to the friction discs 524 for rotation therewith,
will rotate with the pulley body 514. This is the engaged position
of the clutch.
[0068] As illustrated in FIG. 10, the bushing 506 is rotatably
fixed to the drive plate 510. The inner race 516 of the roller
bearing 502 is rotatably fixed to hub 500, and the outer race 518
of the roller bearing 502 is rotatably fixed to pulley body 514.
The bushing 506 and the roller bearing 502 provide radial support
of the pulley body 514 to the hub 500. The bushing 506 allows
relative rotation between the hub 500 and the drive plate 510 and,
by material selection, a controllable portion of Coulomb damping
for the pulley assembly 16.
[0069] The axial expansion of the clutch actuator 508 during
rotation of the pulley body 514 in the predominate rotational
direction actuates the one-way clutch mechanism 504 which couples
the pulley body 514 to the hub 500 to transmit power from a belt
such as belt 30 in FIG. 1 to the input shaft (not shown) of an
accessory. The one-way clutch mechanism 508 includes a plurality of
alternating friction discs 524 and clutch plates 526. Each friction
disc 524 and clutch plate 526 has a bore therethrough to receive
the shaft of the hub 500. The friction discs 524 have an inner
diameter that defines a bore surface that includes a key or keyway
525 for mating engagement with the hub 500 for rotation therewith.
In one embodiment, the friction discs 524 and the hub 500 have a
splined connection. The clutch plate(s) 526 and lower ramp plate
522 include a key, keyway, tabs, splines, cogs 540, or the like on
the surface defining its outer diameter. The cogs 540 are received
between tabs 536 on the holder 528.
[0070] The pulley assembly 16 in FIG. 10, in particular the hub 500
thereof, defines an axis of rotation 600. When the one-way clutch
mechanism 504 is engaged, the pulley body 514 rotates the input
shaft of the accessory. The engaged position is achieved by axial
displacement provided through the relative rotation of the pulley
body 514 and the axial movement of the component(s) of the one-way
clutch mechanism 504 to engage the pulley body 514 with the hub 500
for rotational movement together about the axis of rotation
600.
[0071] During an overrunning condition, the hub 500, and hence the
input shaft, disengages from the pulley body 514 and continues to
rotate with momentum in the first rotational direction (the
predominant direction) when the pulley body 514 experiences a
relative torque reversal or sudden slowdown. In this condition, the
pulley body 514 may continue to rotate in the first rotational
direction but with less angular velocity than the velocity at which
it had been driving the input shaft. The sudden decrease of angular
velocity at the pulley body 514 has the effect of a relative
reversal of torque, which overcomes the bias of the preload spring
530. This results in the aligning of the ramp divots 542 and the
rolling elements 532 traveling into the sockets 542. When the
rolling elements 532 are in the sockets 542 the axial expansion
between the lower ramp plate 522 and the drive plate 510 is
reduced, which relieves the one-way clutch mechanism 504 of the
forces that moved it into the engaged position. As the contact
pressure and friction force between the components of the one-way
clutch mechanism 504 decrease, they will eventually disengage the
one-way clutch mechanism 504, which uncouples the pulley body 514
from the hub 500 so that they can rotate relative to one another
with minimal friction such that the input shaft rotates
independently of the pulley body 514.
[0072] Referring to FIGS. 15 and 16, power input into the pulley
assembly 716 is through the pulley body 704 as it is rotated by its
contact with a belt such as belt 30 in FIG. 1. Power output is
through the hub 700 (that in use may be affixed to a shaft to
operate another device). Support between the pulley body 704 and
the hub 700 includes bearing 702 and cap 710. Cap 710 is fixed to
the pulley body 704 and includes a load support bushing 711 to
allow relative rotation between the hub 700 and the cap 710 and, by
material selection, a controllable portion of Coulomb damping. In
this embodiment, the actuator capable of axial expansion when the
pulley body rotates in a predominant direction is a ball screw
actuator 720, which is disposed about the hub 700. The clutch
mechanism in FIGS. 15-16 is a clutch pack 721 disposed about the
hub and activatable into an engaged position by the axial expansion
of the actuator 720. In another embodiment, the clutch mechanism
may be a cone clutch such as that described above with respect to
FIG. 6.
[0073] Moving from left to right in FIG. 15 the pulley assembly
includes a retaining ring 734, seal 735, a cap 710, a bushing 711,
preload spring 713, springs 750, spring seat 718, ball screw
actuator 720, drive plate 722, clutch pack 721, bushing 730, plate
732, shaft 700, bearing 702, and pulley body 704. The pulley body
704 includes a belt-engaging surface 706. The cap 710 may also
include a secondary seal 735 such as an 0-ring. The springs 713,
750 act to bias components of the pulley assembly 716 axially for
maintained engagement during operation of the pulley. In FIGS.
15-16 the springs 50 are a plurality of Belleville washers. The
number of springs may be varied as well as the material of the
springs to change the characteristics of the pulley assembly as
described above. The ball screw actuator 720 and clutch pack 721
will be described below. The bearing 702 is as described above in
the other embodiments and provides the same advantages.
[0074] As seen in FIG. 16 and the exploded view FIG. 17B, the ball
screw actuator 720 includes a threaded shaft 760 having a nut 762
disposed about the shaft such that the shaft 760 and the nut 762
define a raceway 768 (FIG. 16) for a plurality of rolling elements
764 (FIG. 17B). The ball-screw actuator 720 also includes a ball
tube 766 (FIG. 17B) connecting the bottom of the raceway 782 (FIG.
16) to the top of the raceway 784 (FIG. 16) to recirculate the
rolling elements 764. The threaded shaft 760 is connected to the
drive plate 722. As seen in FIGS. 16 and 17B, the threaded shaft
760 may be seated in a bore 786 of the drive plate 722. The drive
plate 722 includes a key, keyway, tabs, splines, cogs, or the like
725 in or extending from the surface defining its outer diameter.
In the embodiment of FIGS. 15-17B, the drive plate 722 has cogs 723
as part of the outer surface thereof separated from adjacent cogs
723 by gap 725 which is dimensioned to receive the tabs 736 of the
holder 728. As assembled in FIG. 16, the tabs 736 of the holder are
seated in the gaps 725 of the drive plate 722, but the drive plate
722 is able to translate axially relative to the holder 728.
[0075] As seen in FIGS. 17A and 17B, the nut 762 also includes keys
or splines 763 that mate with keyways (not shown) inside the bore
of the pulley body 704. This splined connection (or key-to-keyway
connection) mates the nut 762 to the pulley body 704 for rotation
together about the axis of rotation 749 defined by the shaft
700.
[0076] The clutch mechanism in FIGS. 15-17B is shown as a clutch
pack 721 comprising a plurality of plates of alternating friction
discs 724 and clutch plates 726. In one embodiment, the clutch pack
721 may include just one clutch plate 726 and two friction discs
724 packed into a holder 728. The holder 728 is as described above.
The friction discs 724 are splined (see splines 752) such that they
are connected to the mating splines 701 of the shaft 700 such that
the shaft 700 is rotatably connected to the friction discs 724, but
the friction discs 724 are still free to axially translate relative
to the shaft 700. Accordingly, when the clutch pack 721 is
activated by axial expansion of the ball screw actuator 720, the
friction discs 724 and clutch plates 726 are moved axially into
frictional engagement with one another such that they will rotate
together as a unit.
[0077] As just described, the ball screw actuator 720, during
operation of the pulley assembly, axially expands to activate the
clutch mechanism 721. The nut 762 is keyed to the pulley body 704
for rotation therewith, and when the pulley 704 rotates in the
predominant direction, the nut 762 rotates therewith about the
threaded shaft 760 until the nut 762 has moved axially to an
expanded position that moves the drive plate 722 away from the nut
762 and into engagement with the components of the clutch pack 721.
As a result of the axial movement of the drive plate 722, the
clutch pack components are also moved axially into frictional
engagement with one another. Now, the clutch pack 721 is engaged
and the pulley body 704 and the shaft 700 are connected for
rotation together about the axis of rotation 749.
[0078] Then, when the pulley body 704 rotates in a direction
opposite the predominant direction, for example, experiences a
torque reversal, the clutch pack 721 disengages from the actuator
720 as a result of the actuator 720 rotating with the pulley body
704 and thereby relieving the axial expansion (contracting back to
a non-engaged position) which allows the hub 700 to rotate
independently of the pulley body 704. The hub 700 can continue to
rotate in the predominant direction under its remaining momentum,
which can allow the hub to rotate at speeds greater than speeds of
the pulley body. This is also known as an overrun or freewheel
position.
[0079] In FIGS. 15 and 16, the biasing members 750 are positioned
between the actuator 720 and the cap 710. However, the biasing
members 750 are not limited to this position. In another
embodiment, similar to FIG. 4, the biasing members may be disposed
between the actuator and the clutch mechanism, clutch pack 721.
[0080] Various parameters can affect the operation, responsiveness,
and performance of the pulley assemblies disclosed herein,
including the angle, slope, or profile ramp or camming surfaces,
the coefficients of friction between components in frictional
engagement with one another, and the spring rate of the biasing
member. Other factors that affect the selection of a particular
combination include wear, primary clutching, durability and
cost.
[0081] Overrun torque protection may be provided in all embodiments
herein. However, specific to FIG. 9, overrun torque (drag torque)
is the summation of the preload torque, seal and bearing and/or
bushing drag. Accordingly, the overrun torque is adjustable by
changing the preload spring 530, 713, etc. and through selection of
seals and bushings (i.e., the materials they are made of to alter
the coefficient of friction within the pulley assembly).
[0082] Various embodiments are disclosed herein, and one of skill
in the art should appreciate that the various actuators, clutch
mechanisms and spring configurations can be mixed and matched to
create additional embodiments. Additionally, in one embodiment, the
pulley assembly may be connected to a crank shaft and used to drive
a belt. To operate in such an application, the order of the
components in the pulley assembly are reversed such that the
actuator is connected to the hub (and hence the crank shaft) and
the clutch mechanism in an engaged position links the hub to the
pulley body for simultaneous rotation. Any of the embodiments
disclosed herein or mixed and matched as indicated above as an
option can be "reversed" as just described, so that the pulley
assembly can be mounted to a crank shaft. Here, the pulley body has
a bore and the hub, which defines an axis of rotation, is disposed
within the bore. An actuator, such as a ramp-ramp unit, roller-ramp
unit, ball-ramp unit, cam-follower unit or the like that axially
expand when the hub is rotated in the predominant direction, is
disposed about the hub. Additionally, a clutch mechanism is
disposed about the hub. The clutch mechanism is activated into an
engaged position by the axial expansion of the actuator. In this
engaged position the activation of the clutch mechanism links the
hub to the pulley body for simultaneous rotation in the predominant
direction. Then when the crank shaft experiences a deceleration
(the hub also experiences the deceleration), the pulley assembly
enters an overrun position where the clutch mechanism disengages,
typically as a result of the contraction of the actuator, and
allows the pulley body to rotate at speeds greater than the
hub.
[0083] The embodiments have been described in detail with respect
to the figures presented herein, but it is apparent that numerous
variations and modifications are possible without departing from
the spirit and the scope of the invention as defined in the
following claims.
* * * * *